In a related-art turbofan, a plurality of hollow blades are each constructed by a first surface portion and a second surface portion mounted to the first surface portion. Thus, even when each of the hollow blades has a shape extending axially between a main plate and a side plate in a twisting manner (that is, forms a three-dimensional blade), formation of a hollow space in the blade is promoted, thereby reducing a weight of an impeller (see, for example, Patent Literature 1).